1. Field of the Invention
The invention relates generally to the monitoring of activity of a data processing system and more specifically to the generation of a signal from the monitoring unit to slow up or to stop the clock of a central processing unit.
2. Description of the Prior Art
The throughput of prior art data processing systems was measured by writing software routines and measuring the time it took for the system to execute the routines. When new systems were designed, the same software routines were executed on the new and the old systems and the difference in running time noted. Central processor unit (CPU) limited and peripheral limited software routines were used to compare the throughput of the old and new systems. The execution time of a particular instruction was determined with an oscilloscope. A typical data processing system is described in the "Level 6 Minicomputer Systems Handbook", Order No. CC71, published by Honeywell Information Systems Inc., Waltham, Mass. 02154, copyright Oct. 1978.
Monitoring devices were developed having counters and magnetic tape drives. Typical of these devices is the NCR Comten Model 7916. A typical monitoring device is described in "Dynaprobe 8028 Users Guide", Order No. MP 8028, published by NCR Comten, 1950 W. County Road, St. Paul, Minn., 58113, copyright Nov. 1977. Probes coupled to the monitoring device are placed on the backboard pins of the system being monitored. The signals received by the monitoring device are wired to logic elements such as AND gates, OR gates, inverters and counters to develop performance data. These monitoring devices present a number of problems. Often many signals, each requiring a probe, are needed for the analysis. The pins on the system being monitored are difficult to locate, and the probes easily fall off. The prior art has the requirement of providing probe points for certain signals which increase the system cost.
It is also desirable for customer personnel to take performance measurements, particularly when the customers write their own software. Here the customer must rely on maintenance personnel to determine which backboard signals are needed and to place the probes on the proper backboard pins.
When monitoring the activity of the central processing unit, there is a requirement for slowing down the central processing unit (CPU) in order to monitor a sequence of events or to stop the central processing unit. For example, a trace of all CPU instructions executed and/or a trace of all CPU instruction addresses may be desired. Since present-day monitors are incapable of keeping pace with present-day CPU's, a requirement for slowing down the CPU is now established. There may also be a need to stop the CPU at a particular system event and step slowly through the subsequent cycles. Some of these stop conditions may not be possible to do by software or firmware. These are difficult for maintenance personnel to do from the CPU backplane and relatively impossible for the customer operator to do.